Ischaemic strokes (those caused by blockage in an artery in the brain caused by a blood clot) can be treated with very early use of clot-busting (thrombolytic) drugs to attempt to restore the blood supply and limit the damage, resulting in an increased proportion of people making a recovery to independence after stroke. However, drug treatment only succeed in restoring blood flow in a minority of people with clots in the larger arteries (10-25% depending on the size of the blood vessel) and these people also have the most severe strokes and highest risk of death or dependence as a result of the stroke. Current best treatment is therefore least effective in the group with the most severe strokes. Devices that can be fed through the blood vessels to either remove or break up the blood clot in the brain vessels can open this type of large artery blockage. However, using these devices is a highly skilled procedure and it takes some time both to set up the necessary facilities (including anaesthetic, nurses and medical support) and to reach the blockage. The extra time that is required to use these devices may mean that brain tissue is already irreversibly damaged. If so, then an individual patient cannot benefit and indeed may be harmed by opening the artery. There are no completed clinical trials comparing the outcome in people treated with standard stroke treatment and those treated with devices. PISTE is a randomised, controlled trial to test whether additional mechanical thrombectomy device treatment improves functional outcome in patients with large artery occlusion who are given IV thrombolytic drug treatment as standard care.